The purpose of this project is to demonstrate novel applications of fluorescence spectroscopy in problems of biochemical interest. Recent work has included: 1. The study of the binding of the fluorescent antibiotic pimaricin to red cell membranes by stopped flow fluorescence. Since pimaricin fluorescence enhancement is thought to occur upon binding to membrane cholesterol, the biophasic kinetic plots suggest the presence of two types of cholesterol pools. 2. The rate of labeling of proteins by fluorescent dyes was found to be measurable by stopped-flow fluorescence. Conjugates made by reaction with fluorescamine and quinacrine mustard have higher fluorescence yield than the free dyes. The rates of reaction are altered by competing ligands and modifications of protein structure.